Evaluation of Satellite NO2 Stratospheric Columns with the SAOZ/NDACC UV-Vis Network

J.-P. Pommereau1, F. Goutail1, A. Pazmino1, D. Ionov1,3, F. Hendrick2, and M. Van Roozendael2[1] LATMOS, CNRS, and University of Versailles Saint Quentin, Guyancourt, France[2] Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium[3] Department of Atmospheric Physics, St. Petersburg State University, Russia

NO2 more complex than ozone for several reasons

• Tropospheric contribution larger than for O3 (PBL pollution, Lightning NOx in UTLS)

• Limited information on profile climatology below 20 km and during polar permanent day and night

(models little representative of the troposphere)

• Photochemical diurnal variation

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SAOZ NO2 following NDACC UV-Vis WG recommendations

• Slant columns at sunrise and sunset by zenith sky observations between 86°-91°SZA

• NO2 cross-sections at low temperature (Vandaele et al.)• Slant converted into vertical columns using Air Mass

Factors (AMF) calculated from IASB-BIRA zonal climatologies

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SAOZ network selected stations

Arctic Antarctic Mid-Lat Tropics

SAOZ NO2 PROFILES CLIMATOLOGY

AMF BIRA-IASB look-up tables from:

• Satellite profiles HALOE, POAM III above 20 km (Lambert et al. 2000)

• Complemented below 20 km by SAOZ-B short and long duration balloon profiles at high and middle northern latitudes and the southern tropics

Sunrise Sunset

Ex: northern mid-latitudes

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Comparison with SATELLITES

GOME GDP4, SCIAMACHY Strato (IUPB), OMI Strato (NASA), GOME 2 Strato (IUPB)

• Satellites: nadir viewing, subtraction of modelled tropospheric NO2, correction for clouds (Ghost column)

• SAOZ zenith sky observations less sensitive to PBL tropospheric pollution

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Correction for diurnal photochemical variation

• 1D Photochemical model simulations (stratosphere only)

• Latitude and seasonal dependence

• Satellites columns normalised to SAOZ sunrise column at 90°SZA

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GOME2

ARCTIC: Scoresbysund Greenland (never polluted)

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Diurnal variation corrected

Satellites low biased compared to SAOZ in summer

Original data

SCORESBYSUND

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Not linear. Different behaviour at low and high NO2

Correlation SAT NO2 / SAOZ NO2

Larger noise on GOME

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EXPLANATION: SZA DEPENDENCE

All satellites cut at SZA>85°

GOME less dependent but noisy

Overestimation at high sun, underestimation at low sun(Not SAOZ since always same SZA)

GOME less dependent but noisy

But why underestimation of satellite columns in the summer?

Summer measurements at low sun! From ascending orbit at 21 loc during permanent day instead of descending

orbit at 9 loc. Diurnal variation correction wrong.

SZA at OMI overpass

DUMONT D’URVILLE

Satellites low biased compared to SAOZ

DUMONT D’URVILLESZA DEPENDENCE

Mid-Latitude: Kerguelen (never polluted)

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GOME and OMI high biased in summer, SCIA better but low biased in winter

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SZA DEPENDENCE

But in contrast to polar areas: high sun in the summer and low sun in the winter (daytime orbit only)

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Mid-Latitude: OHP (PBL frequently polluted)

All satellites larger and noisier than SAOZ

SZA DEPENDENCE

Similar to Kerguelen but larger summer high bias and noise on all satellites

Nadir viewing more sensitive to PBL than zenith sky SAOZ

TROPICSLarger SAOZ column in Bauru compared to Reunion

(LNOx during thunderstorm summer, biomass burning and urban pollution in the winter)

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Pastel PhD thesis 2011

BAURUREUNION

Nitrogen Dioxide zonal anomaly between 10-20°S in the summer seen from a circum-navigating long duration

ballon

LNOxLNOx

Pommereau 2007Maximum over Africa and S.America

Satellites: no difference between Bauru and Reunion

Agreement SAT/SAOZ (except GOME)(tropospheric NO2 consistent)

All SAT larger than SAOZ, particularly OMI(wrong tropospheric NO2)

SZA DEPENDENCE

Bauru Reunion

Larger stratospheric columns: Tropospheric ozone underestimated (particularly

OMI and GOME)

Smaller SCIA and GOME2 stratospheric columns:

Tropospheric ozone overestimated.

Systematic seasonal differences (up to 30%) between satellites and SAOZ at all latitudes, attributed to:

• SZA dependences of SAOZ- satellites difference (OMI largest, GOME smallest). Improved correction for diurnal variation and profiles climatology required.

• Errors in tropospheric contributions estimationsTropospheric contribution very difficult to separate in nadir observations

SUMMARY